The objective of this project is to determine whether or not ammonia generated by Helicobacter pylori urease contributes to the formation of nitrate and N-nitroso compounds. A total of 20 patients infected with Helicobacter pylori will be recruited for the study. Study subjects will be given an oral dose of N-urea before and after receiving anti-H. pylori-triple therapy. N-urea is a stable isotope which poses no risk to patients. The concentration of N-nitrate and N-nitrosoproline will be measured in a 24 hour urine specimen on each occasion. A significant decrease of the urinary concentration of these compounds is hypothesized after clearance of the infection.